In a submarine communication system in which an optical communication path is formed undersea and communication is performed, a repeater, for amplifying an attenuated optical signal is provided. In such repeater, maintenance such as replacement, repair, or the like cannot be easily performed. Therefore, the highly reliable repeater is required. However, when the repeater is used for a long period, a failure or the like cannot be avoided. Accordingly, even when some components fail, the repeater has to be able to continue the operation.
For example, in patent document 1, a repeater shown in FIG. 4 is proposed. This repeater includes a drive circuit 101 which drives a pumping light source 102 by a constant drive current, a drive circuit 104 which drives a pumping light source 103 by the drive current according to an inputted variable control signal 110, an optical multiplexer 105 which multiplexes the excitation lights generated by the pumping light sources 102 and 103 and supplies it to a rare earth doped optical fiber 100, an optical demultiplexer 106 which demultiplexes the multiplexed light from the optical multiplexer 105, and a comparator 107 which outputs the variable control signal 110 by which a level of the demultiplexed light is kept constant based on a reference value to the drive circuit 104.
By using such structure, for example, even when the pumping light source 102 deteriorates, by variably controlling the drive current of the pumping light source 103, a problem of a shortening of a life-span of the pumping light source 102 can be coped with. Namely, when the brightness of the excitation light in the pumping light source 102 decreases, the drive circuit 104 operates to increase the brightness of the pumping light source 103 for compensating the decreased amount.
(Patent document 1) Japanese Patent Application Laid-Open No. 2006-128382